Download Engineering seismic evaluation report of the Israel Electric Company

Engineering seismic evaluation report of the Israel Electric
Company office building in Haifa
In collaboration with
Yaron Ophir engineers – Advanced analysis - Resistance to
earthquakes.
March 2011
Table of Contents:
Page
Abstract
1-3
1. General description of the office building
4-5
2. Selecting the existing building performance level
5-6
3. Setting the seismic risk
6
4. The basic assumptions for the analytical testing
7
5. Structure model description
7-19
6. Summary of model analysis
20-25
7. Summary of pushover analysis
8. Summary of analysis in time (time history)
25-27
28-29
9. Summary and conclusions
30
10. Reference
31
Appendix A: Summary of calculations.
Durability test report of IEC office building in Haifa against earthquake
According to American standard guidelines ASCE 41 - 06 and subject to
Israeli Standard 413
Abstract:
This work describes a advanced durability and stability test to horizontal seismic forces of
the IEC office building in Haifa. The tested structure is a reinforced concrete structure with
29 stories above the ground, of height of 120 meters. In addition, the adjacent parking lot,
separated from the main building with a separation joint / interface, is evaluated.
The evaluation for horizontal seismic forces was conducted in a detailed level using linear
analytical tools and methods for the first phase, and non-linear for the second stage, using
advanced computer programs (SAP2000, LUSAS), and according to the instructions of the
advanced American standard (2007) ASCE 41 – 06 which is particularly suitable for testing
and strengthening of existing buildings. The structure tested for earthquake according to
Israeli standard for a recurrence period of 475 years (probability of 10% for occurrence or
stronger acceleration within 50 years). In addition, the structure was also examined for the
earthquake intensity which is stronger than the requirements of the standard, with
recurrence period of 2,475 years (probability of 2% occurrence or stronger acceleration
within 50 years). The design spectrum was built following the standard process of ASCE7 05, which defines the seismic requirement in a similar way to that described in Israeli
standard 413 amendment 3. This requirement is higher than the Israeli standard version of
amendment 2. Figure 1 presents the design curves, which describes the expected horizontal
acceleration (in units of gravity g acceleration) as a function of the period of the structure.
Acceleration spectrum according to standard ASCE7 – 05. Recurrence
period of 1 : 475 years, 5% restraining
Diagram 1 – design spectrum
The performed design was based on:
A. Existing construction and architecture drawings.
B. Existing land and soil reports (Israel Keller office).
The main results of the evaluation of the building for Israeli design quake of 475 years are:
1. According to the evaluation results of the spectral model analysis (linear), the structure is
expected to stand the predicted loads (earthquakes during recurrence period of 475 years,
LS criterion - life saving). In addition, the parking structure adjacent to the building meets
the LS criteria for expected earthquake of recurrence period of 475 years. Garage ceilings
displacements are significantly small than the interface width and pounding / touching
problem between the two buildings is not expected.
2. The evaluation results according to pushover analysis (advanced nonlinear analysis) that
considers the stiffness and bearing capacity of structural elements, and their post-elastic
responses, show that for an earthquake recurrence period of 475 years, failure points for the
various components in the structure, occur after the required pushover limit is reached.
Therefore, the structure and structural components stand firmly in the LS life-saving criteria,
and even in higher – level IO. That means that most of its components will be hurt in a minor
way that would allow the continued functioning of the building (where IO is the level allows
"immediate occupancy" and does not require the interruption of building activity provided
electrical systems, air conditioning, etc., except for structural components are taken care. It
was also found that the structural system stands in the collapse-preventing criterion CP for
shaking with intensity stronger than the appropriate design quake for the recurrence period
of 2475 years.
3. According to the results of the examination for time history analysis (advanced nonlinear
analysis) performed to verify the results of pushover analysis, the result is that the building
stands in the lives saving - LS criteria for the recurrence period of 475 years.
4. The non-structural components: damage to the facade is due to inter floors
displacements. Curtain walls and cladding stones are not expected to have significant
damage, because the inter floors drifts are anticipated to be small - approximately 0.25%,
and the forces acting on them to be smaller than the design load for wind. It should be
noted that other non-structural components (such as electrical systems, air conditioning
systems, pipelines, computer systems, generators, pumps, etc.) were not considered in this
work. If it is necessary to continue the functionality of parts of the building after an
earthquake, it is necessary to ensure their stability during and after the event.
Main conclusions:
In light of the evaluation made it is possible to conclude that the office building is expected
to withstand the predicted earthquake in the recurrence period of 475 years in the life
saving criteria and even beyond it, up to getting close to the higher criteria of
"immediate population". It also expected to withstand the preventing of collapse criteria in
case of strong earthquake of recurrence period of 2475 years.
Attached appendixes: In appendix A, attached the main calculations.
1. General description of the offices building:
Picture 1: General view
The building was constructed more than a decade ago at the southern entrance to
Haifa. It has 29 floors above the ground and 3 floors underneath the ground. The total
height of the tower is 120 meters and it based on a raft foundation. Attached to the
tower are two stories parking building which is separated from the main building by
separation interfaces. The tower has two symmetrical parts connected to each other
every few floors by ceilings or plates or beams. In each side of the building, there are
four massive centered concrete piers (in total eight piers in the building as shown in
diagram 2). In addition to the eight central piers, there are concrete walls in the
building "wings" which provide big stiffness against horizontal forces (surrounded by
blue hexagon at the top of diagram 2). At the perimeter of the building there are round
concrete columns with small section compared to the height of the building (between
0.6 to 1.2 meters). In the piers there is diagonal reinforcement above the entrances
(following updated requirements of the Israeli standard 413), which guaranty ductile
behavior of the coupling beams. This detail was not done in the beams connecting
between the piers and other rigid elements (like wing walls) which functioning in fact
also as coupling beams.
Diagram 2 – shafts and central ruggedness walls marking
2. Choosing the performance level for the existing structure
The performance level for which the structure was evaluated is the level of Life
Safety (LS - Life Safety) for the recurrence period of 475 years. This performance
level is equivalent to the requirements of Israeli standard IS 413. Achieving this
demand gives the structure durability during earthquake without endangering
human life and without collapse, but it expected to receive damages in the structure
(limited cracks and failures) which require repair and examination before returning
people to it and continuing functioning.
In addition, in the non-linear pushover analysis, examined structure response to
unusual seismic event with a recurrence period of 2475 years. The selected
performance level for this earthquake is to prevent collapse (CP - Collapse
Prevention) which ensure no failure will happen in a very strong earthquake.
According to Israeli standard the building was to be tested with important factor I =
1.25 which is load increase of 25% due to the large amount of people located in the
building. Increasing the seismic forces does not necessarily ensure improved
resilience of the building because it depends on limiting the level of damage related
directly to displacement restriction and rotation in its structural components, rather
than the size of the forces. According to standard ASCE41 - 06 the requirement is
rational and straightforward and allows the level of damage limiting (DC - Damage
Control) which is an intermediate level between the level LS (lives saving), and
immediate occupancy level IO which is higher. In our investigation, there is also
reference to a higher level of function as indicated above. In addition, reference was
brought to meet the requirement of important factor I = 1.25.
Table 1: Function level definition of lives saving and collapse prevention according to
ASCE 41 – 06 (2007)
*It should be mentioned that within this frame, a test for function levels of nonstructural systems and components like generators, cooling systems, etc. was not
done (see functional requirements circled in red in the above diagram). Except for
resistance evaluation of the façade of the building.
3. Definition of seismic risk
In the absence of the site survey at this time, the evaluation relied on response
spectrum calculated according to standard requirements of the ASCE7 - 05. The
maximal ground acceleration coefficient predicted in the site is 0.29g for recurrence
period of 2475 years (taken from Israel Standards Institute web site). The procedure
computes the coefficients of the spectrum by this recurrence period, and then the
spectrum is multiplied by 2/3 in order to move back to recurrence period of 475
years.
Based on the ground report including drilling and setting of penetrating of raft
foundation of at least 0.7 meters into hard rock, taken in accordance with the B type
soil (above in accordance with the work plan). In this instance, the vertical vibration,
in the absence of a site survey, we can assume as 2/3 of the size of the horizontal
component **. The spectrum obtained is indicated in figure / diagram 1, including
the recurrence period of 2475 years, and comparison with Israeli standard 413 –
amendment # 3.
4. Analytical evaluation basic assumptions:
Loads
To examine the structure, live loads were loaded on various floors in addition to the
self-weight and other dead loads. These loads were multiplied by a coefficient of
0.25 to be combined with earthquake loads:
• Office floor live load 300 kg \ sq. m.
• The roof of the building live load of 600 kg \ sq. m.
• Lower floors lilve load of 1000 kg \ sq. m.
• The loads on the ceiling between the two parts of the building are listed on the
plans and were taken from them.
Materials
• The concrete strength in the structure ranges from 40 MPa to 60 MPa, and it
marked in the construction drawings. This data was taken into account in
modeling the elements and testing their bearing capacity.
• Reinforcing steel in the structure is standard ribbed steel.
5. Structure model description
To evaluate the seismic response of the structure, it is necessary to build an
analytical model that can describe the behavior of the structure during an
earthquake in a reliable way and calculate the seismic applied loads (displacements,
stresses, shear forces, etc.) expected to develop. Figure / picture 7 describe the
tower structure model.
Features of all the components (flexural rigidity, etc.) are the same as the
component they represent. The moments of inertia are reduced according to ASCE
41 - 06 standard requirements in order to take into account the rigidities of cracked
sections characterizing an existing reinforced concrete structure (see table 2). Threedimensional model of the tower was built by using finite element software
(SAP2000). In addition, a spatial model of the car parking garage was built (finite
element software LUSAS).
Picture 2: View on tower model in finite element software
Picture 3: View on car parking garage model in finite element software
Table 2: Rigidities reduction coefficients according to ASCE 41 - 06 Standard. Table 6-5
amendment of year 2009 (effective rigidities for reinforced concrete sections)
A. Computational assumptions for the model:
The aforementioned building was built about a decade ago, and details of reinforcement
in the hardening components (walls, shafts and coupling beams) opposing the horizontal
forces been evaluated and found capable and with ductile behavioral. For example, in the
cross-sections of piers it was given a diagonal reinforcement over the openings (figure 3),
which ensures the ductile behavior in the coupling beams. This diagonal reinforcement
was not in the beams connecting the two different piers, and coupling beams behavior
will be reviewed in accordance with that.
Diagram 3 – an example to diagonal reinforcement steel above the entrance of shaft 1
ASCE 41 - 06 standard distinguishes between two types of load behavior of horizontal
and vertical concrete components: deformation controlled components and force
controlled components (see Figure 4).
Displacement controlled components (deformed controlled): These are ductile elements
that their displacement region or plastic distortion capcity is twice larger than the linear
displacement / distortion. These ductile components allow consideration of reduction
factor for exciting loads applied in the analysis (gravitation + earthquake) in accordance
with the reinforcement level, element type and type of materials it is made of.
Force controlled components (forced controlled): These are non-ductile components
usually with dominant shear bearing characteristic, in which their displacement region or
plastic distortion is limited and less than twice the linear displacement / distorted region.
In this type of components, the exciting load is combined from the gravitational load,
from which received the worst case with the exciting load from the earthquake according
to the procedure described below.
The structural elements in the structure belong to the displacement-controlled
components and have the ability to develop ductile behavior.
Flexural capacity of the section in bending and shear was calculated using dedicated
software called RESPONSE (2001), which allows to estimate the overall behavior of
concrete component for integrated loads with high accuracy according to its shape,
strength and quantity of reinforcement.
Bending rigidities appropriate to cracked component were taken to assess more reliably
the displacements, shear forces and expected moment that might develop during the
earthquake especially in the early stages of a seismic event in which the level of cracking
in the structural components are relatively low.
Diagram 4: graphical description of components behavior controlled by force and
displacement
B. Assumptions description and modeling in SAP 2000 software


A spatial model of the office building was built. This model consist of line
elements passing through the centers of stiffness of the component they
represent. The geometry data of each section where entered into the software,
including walls and shafts.
Between the vertical lines representing the spatial elements, and the real border
of those elements connecting rigid elements. The modeling principle is described
in Figure 5.
Diagram 5 – Line modeling principal of walls and cores (Paulay & Priestley, 1992)
• In the lower levels of the structure, there are many shear walls that stiffens the
structure in these floors. In the calculation model two walls were given to each main
direction representing the stiffness and bearing capacity of existing walls of these
levels.
• The structure is based on a raft foundation poured onto the rock. Accordingly, the
model assumed full connection of the structure to the soil, and do not take into
account the interaction between the structure and the ground. This assumption
produces larger loads that are transferred to the structure and in this case, it is a
conservative assumption.
C. The analytical tools for engineered functional design:
The American standard ASCE 41 - 06 defines several methods for calculating existing
structures for earthquake loads. These methods can be divided to linear (equivalent
static analysis, spectral modal analysis that belongs to a group of linear dynamic analysis)
and nonlinear methods (non-linear static analysis and nonlinear dynamic analysis).
Calculation methods chosen are in the first stage, the structure calculation using linear
spectral modal analysis used as reference and helps in understanding the behavior of the
office tower, and in the second phase structure calculation using pushover nonlinear
static analysis, and testing is using non-linear dynamic analysis (Time History).
D. Description of the modal analysis
Spectral modal analyzes were made for three main directions Y, X (horizontal directions)
and Z (vertical direction) of the building. The dynamic characteristic of the structure were
calculated in all directions: periods and effective modal masses of vibration modes.
Displacements, shear forces and bending moments were calculated by the SRSS method
(root sum of the squares). The analysis was made for the possible combinations *:
• One hundred percent force from X direction + 30% force from Y direction + self-weight.
• One hundred percent force from Y direction + 30% force from X direction + self-weight.
* It should be noted that these combinations are more severe than required by Israeli
standards.
Details of the spectrum used for analysis appears in section 3.
E. Pushover analysis description
To evaluate the non-linear seismic response of the structure in a reliable way, it is
necessary to build an analytical model that can describe the behavior of the structure and
its components in an earthquake and calculate seismic exciting stresses likely to develop
(displacements, moments, shear forces, etc.). Before performing a nonlinear analysis, it is
necessary to define the non-linear properties of building components (explanation for
this pushover analysis in shown in section F).
In the spatial model built to represent the structure, the following was considered:
• Behavior of concrete piers in bending, and that while taking into account the sections
bearings capacity according to the direction of their horizontal loading, and tension /
pressure developed in them due to the global behavior of the building.
• Behavior of concrete beams, connecting between the stiff elements in the structure
and function as coupling beams (Coupling Beams).
Since in the longitudinal direction the tower bearing capacity and stiffness are very big,
pushover analysis was performed only in the transverse direction. In order to perform a
pushover analysis, the same model used in modal analysis was used. In the main piers
and in the coupling beams, the nonlinear behavior was defined by calculating the bearing
capacity of the sections using RESPONSE 2000 software (see example for equivalent
section to one of the piers represented in figure 6), were first calculated to gravity loads
in service mode and then, to loading conditions developing during the earthquake and
changing during its operation (i.e., an increase in horizontal load causing increase in
bending and shear in certain ratio corresponding to each of the components in
accordance with its schema and change in axil exciting loads depending on the direction
of action of the earthquake). Distinctions was made between sections with pressure
force and sections with tension loading were made, and their bearing was entered to the
program accordingly. Into the SAP finite elements software were input all the yielding
capacities and failure capacities as calculated in RESPONSE software for each of the
components (see example in figure 7). In addition, the behavior of the hinge according to
guidelines of standard ASCE41 - 06 was input into the software (see table 3). The
pushover was made according to the first mode of vibration in the transverse direction
(mode 5 as described in main results of modal analysis).
Diagram 6 – an example for shaft 1 bearing calculation in the pushover side
Diagram 7 – an example of chapter modeling in shaft 1 as entered into the finite
elements software
Table 3 – definitions and requirements of standard ASCE41 – 06 for modeling and
determination of functioning level according to plastic circles for concrete walls
F. Nonlinear static analysis (pushover analysis):
Out of the existing calculation methods, undoubtedly the most popular method
developed as a tool for the functional design is the non-linear static pushover analysis
(Pushover Analysis) because of its relative simplicity and reliability, and therefore it is
being used here.
The pushover analysis is a method for assessing nonlinear behavior of the structure, in
which the strength and deformation requirements estimated by nonlinear material
(sectional repeat) incremental horizontal static analysis. In the approach used here, static
loads, which represent approximate inertial forces that develop during the earthquake
applied by a predetermined distribution. In the analysis made here, distribution of loads
fits to the first mode in the transverse direction (mode 5), as received from the modal
analysis. The structure is excited to the point where yielding is received in most or all
components of the system resisting to horizontal loads (diagonal in concrete, soil and
foundation system). The pushover curve describes the shear force at the base of the
structure as a function of displacement in the structure top. An example of a pushover
curve is given in figure 8. For example, in the curve shown in figure 8 several structural
function levels are indicated, which can be a functional requirement definition for the
structure. If the overall displacement at the reference point for a defined requirement is
obtained on the curve to the left of the line defined as a required function criterion, the
building meet the demand. If the displacement was to the right of the line, then the
structure does not meet the demand.
With the obtained pushover curve and the response spectrum, the building's function
point is calculated: the point of equilibrium between demands (spectrum) to the
structure bearing (pushover curve). Here we use the approach described in the US (2007)
ASCE 41 - 06 document. The function point provides estimation to the expected seismic
response level of the structure for a given demand and at this stage it should be tested
whether the structure function point meets the design objectives such as: displacements,
ductility rate and plastic deformation in various hardening components. In fact, the
function point is the point to which the structure should reach without failure.
Pushover analysis advantages
1. Evaluation of non-linear response of the structure and the system bearing capacity to
horizontal forces in realistic way (as opposed to a standard linear analysis).
2. Evaluation of the order of failures development and assessment in structural
components and expected damage assessment of them (ductility rate assessment).
3. Evaluation of shear forces, forces in the components of the structure, displacements
and drifts.
Pushover analysis disadvantages
The Pushover analysis performed on the structure considers only the shape of the first
vibration mode only (main vibration shape), and does not consider contributions of
higher vibration modes. More details about the system performance principles,
advantages and limitations are shown in the US document ASCE 41 - 06 (2007).
Diagram 8 – main structural function levels defined on top of the pushover curve: vertical
axis describe the structure top displacement, and the horizontal axis describe the shear
force at the structure base
Immediate occupancy: limited damage, structure and essential systems keep functioning
Life safety: damage to structure components but not in a level that will bring the
structure into collapse
Collapse prevention: level in which the structure is on the verge of collapse
G. Time history analysis description (Time history)
The pushover analysis is performed according to the first mode of vibration in the
transverse direction, and does not take into account the higher mode influences.
Therefore, time history analysis performed in order to ensure that the pushover analysis
results are reliable.
In this analysis, vibration record in time is applied on the base of the structure, , and
structure components response in time is analyzed. This analysis is a nonlinear analysis,
and was performed on the same model as the pushover analysis was applied. Since site
specific survey was not carried out in the location of the building, we did not have any
records of earthquakes to be used the analysis in time. Therefore, an artificial earthquake
adjustment was made, which was created using commercial software (SIMQKE). The
earthquake has compatibility to the predicted PGA in site, and to acceleration and
displacements spectrum with recurrence period of 475 years. This vibration is considered
as a severe vibration because it excites all major mods of horizontal vibration in the
structure (suitable to the design spectrum throughout all periods).
Diagram 9 – time hisotry record of artificial vibration accelerations
Diagram 10 – vibration accelerations spectrum in comparison to design spectrum
Diagram 11 – vibration displacement spectrum in comparison to design spectrum
6.
Main results of linear spectral modal analysis in the evaluation
the office building for earthquake:
Diagram 12 – description of the structure modal in finite elements software
A. Vibration modes received:
Table 4 – modal vibration shapes
B. Main vibration shapes
Mode 5 – vibration in the transverse direction (Y), period T = 3.2 sec
Mode 6 – vibration in the longitudinal direction (X), period T = 1.7 sec
Mode 8 – vibration in the transverse direction (Y), period T = 0.7 sec
Mode 9 – vibration in the longitudinal direction (X), period T = 0.4 sec
C. Forces obtained in the building (without reduction factors):
Table 5 – summary of spectral modal analysis forces
The results shown in the table are without reduction factors. In the evaluation
according to ASCE 41 – 06 standard, the reduction factors are compatible to discrete
components and are not global to the structure.
D. Displacements in the tower:
Table 6 shows the displacements received from the spectral modal analysis in the
transverse and longitudinal directions. The inter floor drift is calculated. The maximal
inter floor displacement value obtained is 0.28%, The upper values according to
ASCE 41 - 06 standard is 1% for IO service level, and 2% for LS service level. (For
comparison, the Israeli standard 413 requirement for this structure is equal to 0.4%).
Inter floor
drift
Inter floor
drift
floor
ent
ent
ent
Table 6 – inter floor displacements summary (drift)
E. Cross sectional bearing capacity
In the following table the examinations made to various elements in the tower and
parking are summarized. For each cross-section, a DCR ratio is described: Demand /
Capacity ratio. When the value is greater than 1.0, the examined section does not
stand in the applied loads. In the DCR calculations the reduction factor is considered
adjusted to the element under consideration (wall, pillar) and way of loading and
reinforcement in it. It is more accurately express the ability to enter into the plastic
zone behavior. Calculation presented here is for the LS criterion for recurrence period
of 475 years.
In addition it is showing a column where DCR ratio is calculated for increased load
corresponding to important factor of I = 1.25 of the Israeli standards to the
occupancy of the building. The ASCE 41 - 06 standard does not check by such
amplification factor, but requires the use of higher criterion; this column is presented
as a reference to the Israeli standard requirements. In the table there is als reference
to the results obtained for the car parking.
Summary of tested elements:
DCR *
Displacements
Pier 1
Pier 2
Pier 3
Pier 4
Pole / pillar D = 120
Pole / pillar D = 100
Pole / pillar D = 80
Pole / pillar D = 60
Test for coupling beams
30 / 90
T
Test for the parking
Displacements
Dangerous pillar bearing
0.13
0.32
0.53
0.26
0.30
0.32
0.22
0.61
0.20
DCR * (I = 1.25)
0/17
0/40
0/66
0.32
0.38
0.40
0.27
0.76
0.26
0.61
0.52
0.77
0.65
0.001
0.77
---
Table 7 – summary of spectral modal analysis results
*DCR ratio: Demand / capacity ratio (if smaller than 1.0 – safe)
7. Main pushover analysis results:
Pushover analysis was performed in the transverse direction of the structure in its
current condition considering the vertical load exerted by the weight of the building, and
taking into account the effect of the vertical component of the response spectrum in a
rate of 30%. It was performed by two alternatives:
1. It acts in gravitational acceleration direction (gravity loads are added).
2. It acts contrary to the direction of gravitational acceleration (decreased from the
gravitation load).
This test was done to examine the effect of the load combination on the analysis due to
building proximity to the fracture, and the likely possibility that it will experience
vibrations in the vertical direction during a close seismic event. Figure 14 shows that
function point has not changed significantly between the two cases described above.
Pushover curves describing the shear stress at the base of the structure, as a function of
the movement of the structure top, are presented in figures 13 and 14. The function
points are described on the pushover curves for a seismic event with recurrence period
of 475 years and for the fatal event from the corresponding recurrence period of 2475
years (considering 5 % damping), including failure scenarios (yielding) expected to
develop in the structure components in the order of their development and can be
summarized as follows:
1. Beginning of bending of walls in pier 3 (followed by yielding of pier 1).
2. The start of the yielding of the coupling beams (see figure 15).
3. The failure in the coupling beams.
The main failure scenarios are obtained after the function point (right to it on the
curve), and therefore the structure is durable for design excitation for 475 years and
even from more severe exciatation (2475 years).
Pushover analysis results are detailed in Appendix A.
Yielding start at shaft 3
Start of Yielding in coupling beams
Yielding start at pier 1
Start of failure in coupling beams
Diagram 13 – pushover curve in the transverse direction of the structure including
function points and failure scenarios
Figure 14 – pushover curve comparison of a case in which the vertical component of the
vibration is acting upwards (opposite to gravity forces), and a case in which the
component acts downwards
Start of yielding in
coupling beams
Failure in tension in soil in
the structure perimeter
yielding start at
shaft 3
Diagram 15 – Location of beams and piers that yield first
8. Main results of time history analysis:
Performing non-linear analysis in time, enable us to receive the high influence of the high
modes that increase the total shear forces in the structure base, but decrease the
displacements at the structure top (in relation to pushover analysis). In diagrams 16 and
17 the forces are shown at the tower base and the displacements at the top respectively.
The big difference in the shear forces in the base of the building is because the pushover
is suitable to the first mode of the building, while the second mode has big impact on
shear forces. In terms of forces in the elements it is shown that the structure does not
pass its bearing capacities, and that all the examined sections meet the IO criteria for the
tested vibration (suitable recurrence period of 475 years).
For example, figure 18 presents the behavior of the coupling beam cross section during
earthquake. One can see passing of yielding load, but without the passing the plastic
rotation, which is defined for IO criteria (marked with a blue dot on the graph).
Diagram 16 – horizontal force in transverse direction at the base of the structure as a
function of time (in dashed line a comparison to pushover analysis)
Diagram 17 - transverse displacement at the top of the structure as a function of time (in
dashed line a comparison to pushover analysis)
Diagram 18 – segment behavior in the coupling beam in the time history analysis
9. Summary and conclusions
The evaluation results presented in accordance with the American document and in
accordance with the loads specified in the beginning of this document, show that the
office building of IEC is durable to earthquake with a recurrence period of 475 years in its
current state for LS criterion and also meets higher demand for immediate occupancy
(IO) with minor damages only (minor cracks start at the bottom of piers 1, 3 and coupling
beams in the structure north and south wings). It also durable strong excitation of the
structure with recurrence period of 2475 years and in preventing collapse (CP) criteria. It
should be noted that the examination was performed according to the standard
spectrum only.
Since the site is located near the fault, there is a place to consider performing a specific
site survey to get more rational seismic load definition than the one appears in the
standard general map (not required by the Israeli standard on this site).
10. References

ASCE/SEI 41-06 (2007). "Seismic Rehabilitation of Existing Buildings". American
Society of Civil Engineers.

LUSAS (2010). Finite Element Analysis Software, Version 14.3. Kingston upon
Thames, United Kingdom.

SAP2000 (2010) Finite Element analysis Software, Version 14.2-4 Computers and
structures Inc. Berkeley Ca.

Response-2000 (2001). Reinforced Concrete Sectional Analysis. Version 1.0.5,
Written by Dr. C. Evan Bentz as part of project supervised by Professor Michel P.
Collins, University of Toronto 2001.
Sincerely,
Korban Co. Engineering Ltd.
20.03.2011
Appendix A: Main calculations
Modal analysis
Planning for an earthquake - risk assessment - the dynamics of structures - bridges –
Infrastructure
Yaron Ofir Engineering LTD.
Haifa 20 Jan 2011
Subject: IEC Office building, Haifa
Structure description
-
-
The tested structure is a concrete office building with 29 floors (above ground level)
with a height of 120 meters. Typical floor height is about 4.1 meters.
The structure consists of two main parts (marked with blue color in the sketch),
connected to each other with paved ceilings. Place and size of connections is
changing between structure floors.
The structure based in the rock with a raft foundation.
Around the building, there are two stories parking lots, separated by a joint from the
tower.
Basic data and assumptions for modal analysis of the office building (according to
ASCE 41 – 06 FEMA 356):
-
Structure modeling done according to existing architecture and construction plans.
Concrete structure B – 40 to B – 60 according to construction plans.
Polygon Iron in the structure according to construction plans.
Rigidity and soil bearing capacity according to report made by Keler office for base
above the raft foundation.
No need to consider the P - ∆ effect due to low inter floor displacement – need
confirmation during the calculation phase.
Assumptions in structure modeling:
-
In the structure analysis, reduced rigidity / stiffness of the cracked concrete
components was taken into account according to update chart for standard ASCE 41
– 06. Poles / pillars cross sections, beams and walls rigidity reduced as shown in
table 6 – 5:
According to paragraph 6.7.2.2, the coupling beam rigidity in the shafts is according to the
behavior of unpaved beam:
-
-
-
Service loads:
Useful load of office floors
300 [kg / m²]
Roof useful load
600 [kg / m²]
Useful load of lower floors
1000 [kg / m²]
Useful load of mid ceilings according to plans of S. Angel office, flooring thickness as
in architecture plans - 7 cm.
Beams at the perimeter:
Curtain walls 8 mm of glass
21.6 [kg / m²]
Stone walls of 3 cm thickness
81.0 [kg / m²]
According to ground report request (Israel Keler office 4 Jan 2000), raft foundation
penetrate at least 0.7 m into hard continuous rock. Ground classification according
to Israeli standard 413, correction sheet # 3 is B (expressed in the construction
plans).
In order to calculate the earthquake loads, spectrum calculated according to
standard ASCE 7 – 05, multiple by 2/3 for a recurrence period of 475 years. The
spectrum values are close to the values received in Israeli standard 413, correction
sheet # 3.
Acceleration spectrum according to standard ASCE 7 – 05, recurrence period of
1:475 years, 5% restrain.
Structure model in finite elements software:
The model is spatial and consist of line elements only – pillars, walls and shafts. It is modeled
as line elements with joints and connections between them in the levels.
In the diagram, one can see the shafts modeling in dark grey color with rigid connections to
their geometric end in black color. Pillars marked in light blue, beams in light grey and
stiffness in the levels marked in green (instead of a ceiling).
Loads:
Half floor full model was built, including flooring thickness, additional fixed loads and useful
loads.
Loads received from this model used for specific mass distribution for the lined structure
height:
In connecting ceilings between the structure parts, load given according to paved ceiling
plans.
Main oscillation forms:
Mode 8: T = 0.7 sec
Mode 5: T = 3.2 sec
Mode 9: T = 0.4 sec
Mode 6: T = 1.7 sec
Spectral model analysis:
The results of the Spectral model analysis (according to spectrum already presented):
Forces: Forces are before reduction coefficients
self weight
X direction
Y direction
Inter floor displacements:
Floor #
Maximal inter floor displacement is marked. It is possible to notice that in the transverse
direction, maximal inter floor displacement is bigger – in the direction which the structure is
more flexible.
Given displacements are very small – the structure is relatively rigid.
For LS criterion – 2% of displacement allowed. For IO 1% is allowed. (ASCE 41 – 06).
Forces combination:
The structure tested for two load combinations:
1.0 SW + 1.0 EQ x + 0.3 EQ y
1.0 SW + 0.3 EQ x + 1.0 EQ y
Shafts testing: Shafts marking
Shaft 1: maximal momentum received at shaft bottom
m – factor reduction factor relevant to the tested component, according to standard ASCE
41 – 06.
DCR ratio between demand and bearing capacity of the tested section. When smaller than
1.0 the section compatible with standard requirements.
Combined combination of disturbing loads in main directions of the section according to
the standard. Section is OK when smaller than 1.0
An example for bearing capacity calculation for shaft section, test in Y direction:
Maximal shear in level 8.77
Test in X direction
Test in Y direction
Maximal momentum in Y direction
Test in X direction
Test in Y direction
Shaft 2: maximal momentum received at shaft bottom
Test in X direction
Test in Y direction
Shaft 3: maximal momentum received at shaft bottom
Test in X direction
Test in Y direction
Shaft 4: maximal momentum received at shaft bottom
Test in X direction
Test in Y direction
Test for maximal momentum in Y direction
Test in X direction
Pillar D = 120
Test in Y direction
Pillar D = 100
Pillar D = 80
Pillar D = 60
Coupling beams test:
a. 30 / 190 beam test between shaft 3 and shaft 2
b. Beam test between shaft 2 and pillars in the perimeter
Parking lot test:
The parking lot has two floors, paved hollow plates ceilings on pillars and casted concrete
beams in site. In outer parts, rigid concrete walls (marked with purple lines) and separation
joint (light blue) divide it to two parts. In addition, there is separation joint between the
parking lot and the office tower.
Two square cross sections of rigid walls in relation to the frames are in the building
structure, which will cause torsion because of the distance between the center of mass and
the center of rigidity. The test done for pillars marked in RED, in areas with the maximal
displacement.
Assumption of
vibration loads according to weighted static analysis following the ASCE 41 – 06 process.
Load Assessment:
Self-weight
useful load
combination
[ton / m²]
[ton / m²]
Floor 1: Paved board ceiling D = 18 + 6
0.466
0.25
0.54
Floor 2: Paved board ceiling D = 30 + 10
0.704
0.5
0.85
Load combination – self-weight + 0.3 useful load
Cycle time assessment:
Total shear force determination:
Seismic load division to height:
Mass
Height
Himi
Himi / ƩHimi
Floor 1:
Floor 2:
Horizontal load on the floors:
Floor 1:
1.78 [KN / m²]
Floor 2:
5.63 [KN / m²]
Spatial model built in finite elements software. Self-weight and horizontal loads added.
Bending rigidity of the sections reduced 0.5 EI.
Loads combinations according to 100% x + 30% y or 30% x + 100% y
a. Displacements:
Maximal displacement received in the roof floor, in the separation joint area
between the two parts of the parking lot (marked with purple):
Calculation of inter floor displacement:
It can be seen that inter floor displacement is negligible.
Test for forces in the pillar: test for the pillar in area with big displacements:
Summary of tested elements
DCR *
DCR * (I = 1.25)
Displacements
0.13
0.17
Shaft 1
0.32
0.40
Shaft 2
0.53
0.66
Shaft 3
0.26
0.32
Shaft 4
0.30
0.38
Pillar D = 120
0.32
0.40
Pillar D = 100
0.22
0.27
Pillar D = 80
0.61
0.76
Pillar D = 60
0.20
0.26
Test for coupling beams
30 / 90
0.61
0.77
T
0.52
0.65
Test for parking lot
Displacements
0.001
-- not relevant to parking
Dangerous pillar bearing capacity
0.77
-- not relevant to parking
*DCR factor describes the ratio between active loads to bearing capacity. When
smaller than 1.0, element tested OK.
Column DCR = 1.25 estimates tested sections rigidity according to spectrum
amplification (as in Israeli standard 413). In standard ASCE 41 – 06 the requirement
is different – functioning requirement will determine the DCR accordingly.
Nonlinear pushover analysis
Shaft 1 (RC shear walls)
Pushed side 1A
Stretched side 1B
Pressure addition vertical component vibration 1035435.0 1.070
1.061
574000.0
Pressure reduction vertical component vibration 900820.0 0.931
0.936
506180.0
Shaft 2 (RC shear walls)
Pushed side 2A
Shaft 3 (RC shear walls)
Stretched side 2B
Pushed side 3A
Stretched side 3B
Shaft 4 (RC shear walls)
Pushed side 4A
Stretched side 4B
Non-linear modeling of concrete shaft (RC shear walls)
Nonlinear modeling of concrete shaft (RC shear walls)
Nonlinear modeling of coupling beams (RC coupling beams)
Nonlinear modeling of coupling beams (RC coupling beams)
Built spectrum according to standard ASCE 7 – 05. See details in modeling test.
submission start at shaft 3
submission start coupling beams
submission start at shaft 1
destruction start at coupling beams
Submission start at shaft 3
Submission start coupling
beams
Submission start at shaft 1
Destruction start at coupling
beams
Testing the vertical component influence on function point
Time history analysis
Because there is no site survey, for creation of artificial vibration, we use the SIMQKE
software. It was done according to spectrum presented in linear analysis. The vibration is
according to the spectrum along all cycle times; therefore, mostly the vibration will be
worse.
Vibration recording:
The vibration spectrum in comparison to design spectrum – acceleration spectrum:
The vibration spectrum in comparison to design spectrum – displacement spectrum:
a. Shear forces in the base
Maximal forces: 58189 KN,
-47776 KN
b. Displacements at the structure top
Maximal displacements: 32 cm, -29 cm
c. Position of plastic joints in the structure during maximal force
It is clear that all joints positioned in the coupling beams. The joints remain in the IO
criteria domain.
d. Position of plastic joints in the structure during maximal displacement
It is clear that all joints positioned in the coupling beams. The joints remain in the IO
criteria domain.
e. Description of joints entering into the elastic domain
Presentation of represented joints that getting close to the elastic domain more
than others.
Joint in bottom of shaft 3 – no submission
Joint in coupling beam – reach submission point but stay at allowed IO criteria
domain